Submitted on November 12, 2008
Revised on December 24, 2008
Accepted on January 15, 2009
Frontal and motor cortex oxygenation during maximal exercise in normoxia and hypoxia
Andrew W. Subudhi1*, Brittany R. Miramon1, Matthew E. Granger1, and Robert C. Roach2
1 University of Colorado at Colorado Springs
2 University of Colorado Health Sciences Center
* To whom correspondence should be addressed. E-mail: asubudhi{at}uccs.edu.
Reductions in prefrontal oxygenation near maximal exertion may limit exercise performance by impairing executive functions that influence the decision to stop exercising; however, it is unknown if deoxygenation also occurs in motor regions that more directly affect central motor drive. Methods Multichannel near infrared spectroscopy (NIRS) was used to compare changes in prefrontal, premotor and motor cortices during exhaustive exercise. Twenty-three subjects performed two sequential, incremental cycle tests (25 W.min-1 ramp) during acute hypoxia (PIO2 = 79 mmHg) and normoxia (PIO2 = 117 mmHg) in an environmental chamber. Test order was balanced and subjects were blinded to chamber pressure. Results In normoxia, bilateral prefrontal oxygenation was maintained during low- and moderate- intensity exercise, but dropped 9.0 ± 10.7 % (mean ± SD; P < 0.05) prior to exhaustion (maximal power = 305 ± 52 W). The pattern and magnitude of deoxygenation was similar in prefrontal, premotor and motor regions (R2 > 0.94). In hypoxia, prefrontal oxygenation was reduced 11.1 ± 14.3% at rest (P < 0.01) and fell another 26.5 ± 19.5% (P < 0.01) at exhaustion (maximal power = 256 ± 38 W, P < 0.01). Correlations between regions were high (R2 > 0.61), but deoxygenation was greater in prefrontal than in premotor and motor regions (P < 0.05). Conclusions Prefrontal, premotor and motor cortex deoxygenation during high-intensity exercise may contribute to an integrative decision to stop exercise. The accelerated rate of cortical deoxygenation in hypoxia may hasten this effect.
